This invention relates to x-ray lithography, and more particularly to an electron gun assembly suitable for use therewith.
Heretofore, various types of lithography have been used in the manufacture of integrated semiconductor circuits. Photoresist was deposited on the surface of a semiconductor wafer and then the wafer was optically exposed. However, as a result of the requirement for miniaturization, lithography has progressed toward shorter and shorter wavelengths, which are necessary to provide good resolution and small feature size. X-ray lithography has been proposed as a solution to the resolution problem because it has particularly short wavelengths. In such lithography, a mask, having the desired pattern thereon, is interposed between the source of radiation and the semiconductor substrate with the resist on which the pattern is to be exposed.
A high power density electron source is needed for soft x-ray generation such as, for example, 20 kW at 10 kV into a 1 mm spot diameter, which preferably is variable. Heretofore, diodes of the preferred annular form did not provide enough current at low target potential. Triodes have been considered, but they suffer from complexity of fabrication, more complicated and better regulated power supplies, overheating of the intermediate anode by backscattered electrons, and difficulties in cooling the electrodes and supporting insulators.
It is an object of the present invention to provide a new and improved electron gun assembly, which is particularly adapted, among other possible uses, for use in x-ray lithography, which overcomes or at least mitigates a number of the above-identified problems of the prior art gun assemblies, and which has high diode perveance.